The degranulation of cultured mouse mucosal mast cells and rat peritoneal mast cells, but not human basophils, is inhibited by the drug sulphasalazine, used to treat inflammatory bowel disease. N-acetyl cysteine, given as a mucolytic agent in asthma and to treat acetomenophen overdose, has been shown to directly degranulate mast cells and basophils. This may help explain some adverse reactions to this drug. Mast cells, obtained from monkey gastrointestinal tissues, degranulate to immunologic stimuli and ionophores, but not to compound 48/80. Histamine release is inhibited by theophylline. Patients with a history of immediate adverse reactions to foods and whose symptoms are reproduced on challenge, are atopic, have multiple positive skin tests to foods and inhalants, have a positive skin test to the food in question, and by history are those with the most severe reactions. To date, approximately twenty-five patients with idiopathic anaphylaxis, and four with systemic mastocytosis have been challenged with sulfites. No clinical reactions have been observed, although plasma histamines elevated in three out of four patients with systemic mastocytosis. Patients receiving ATG had a rise in ATG-specific IgE.